Multi-institutional comparison of secondary check of treatment planning using computer-based independent dose calculation for non-C-arm linear accelerators.

PURPOSE: This report covers the first multi-institutional study of independent monitor unit (MU)/dose calculation verification for the CyberKnife, Vero4DRT, and TomoTherapy radiotherapy delivery systems. METHODS: A total of 973 clinical treatment plans were collected from 12 institutions. Commercial software employing the Clarkson algorithm was used for verification after a measurement validation study, and the doses from the treatment planning systems (TPSs) and verification programs were compared on the basis of the mean value ±â€¯two standard deviations. The impact of heterogeneous conditions was assessed in two types of sites: non-lung and lung. RESULTS: The dose difference for all locations was 0.5 ±â€¯7.2%. There was a statistically significant difference (P < 0.01) in dose difference between non-lung (-0.3 ±â€¯4.4%) and lung sites (3.5 ±â€¯6.7%). Inter-institutional comparisons showed that various systematic differences were associated with the proportion of different treatment sites and heterogeneity correction. CONCLUSIONS: This multi-institutional comparison should help to determine the departmental action levels for CyberKnife, Vero4DRT, and TomoTherapy, as patient populations and treatment sites may vary between the modalities. An action level of ±5% could be considered for intensity-modulated radiation therapy (IMRT), non-IMRT, and volumetric modulated arc radiotherapy using these modalities in homogenous and heterogeneous conditions with a large treatment field applied to a large region of homogeneous media. There were larger systematic differences in heterogeneous conditions with a small treatment field because of differences in heterogeneity correction with the different dose calculation algorithms of the primary TPS and verification program.

Effectiveness of a simple and real-time baseline shift monitoring system during stereotactic body radiation therapy of lung tumors.

PURPOSE: This study aimed to clinically validate a simple real-time baseline shift monitoring system in a prospective study of consecutive patients undergoing stereotactic body radiation therapy (SBRT) of lung tumors, and to investigate baseline shift due to intrafraction motion of the patient's body during lung SBRT. METHODS: Ten consecutive patients with peripheral lung tumors were treated by SBRT consisting of four fractions of 12 Gy each, with a total dose of 48 Gy. During treatment, each patient's geometric displacement in the anterior-posterior and left-right directions (the baseline shift) was measured using a real-time monitoring webcam system. Displacement between the start and end of treatment was measured using an X-ray fluoroscopic imaging system. The displacement measurements of the two systems were compared, and the measurements of baseline shift acquired by the monitoring system during treatment were analyzed for all patients. RESULTS: There was no significant deviation between the monitoring system and the X-ray imaging system, with the accuracy of measurement being within 1 mm. Measurements using the monitoring system showed that 7 min of treatment generated displacements of more than 1 mm in 50% of the patients. CONCLUSIONS: Baseline shift of a patient's body may be measured accurately in real time, using a monitoring system without X-ray exposure. The manubrium of the sternum is a good location for measuring the baseline shift of a patient's body at all times. The real-time monitoring system may be useful for measuring the baseline shift of a patient's body independently of a gating system.

Technical note: determination of the optimized image processing and template matching techniques for a patient intrafraction motion monitoring system.

PURPOSE: In this work, the authors determine the optimal template matching method and selection of pixel data for use in a system for monitoring patient intrafraction motion. METHODS: The motion monitoring system is based on optical tracking of a marker block placed on the patient. The temporal resolution of the system was evaluated with a respiratory motion phantom. The phantom moved the marker with a peak-to-peak amplitude of 0.6-4.0 cm and a period of 1, 3, and 6 s. Three template matching methods were applied: Sum of squared difference (SSD), sum of absolute difference (SAD), and normalized cross-correlation (NCC) using each of four pixel color data schemes (RGB and gray level modified by one of three image processing steps). An in-house algorithm called auto region-of-interest (AutoROI) automatically reset the marker detection region-of-interest to improve the calculation speed. RESULTS: RGB and gray level temporal resolutions were 54.22 ± 10.81 (1 SD) s and 12.70 ± 3.87 (1 SD) s, respectively. The temporal resolution when using SSD and SAD was higher than when using NCC. Positional accuracy was within 1 mm. Both values were within the tolerance specified by AAPM Task Group 142. To avoid misidentification of the marker, a threshold-based self-validation within the marker recognition system was implemented and was found to improve the tracking of motion with a high amplitude and short period. CONCLUSIONS: An intrafraction motion monitoring system using SSD or SAD and applied to gray pixel data can achieve high temporal resolution and positional accuracy.